Mesenchymal stem cells improve cardiac conduction by upregulation of connexin 43 through paracrine signaling

Mureli S, Gans CP, Bare DJ, Geenen DL, Kumar NM, Banach K. Mesenchymal stem cells improve cardiac conduction by upregulation of connexin 43 through paracrine signaling. Am J Physiol Heart Circ Physiol 304: H600-H609, 2013. First published December 15, 2012; doi:10.1152/ajpheart.00533.2012.-Mesenchymal stem cells (MSCs) were shown to improve cell survival and alleviate cardiac arrhythmias when transplanted into cardiac tissue; however, little is known about the mechanism by which MSCs modify the electrophysiological properties of cardiac tissue. We aimed to distinguish the influence of cell-cell coupling between myocytes and MSCs from that of MSC-derived paracrine factors on the spontaneous activity and conduction velocity (theta) of multicellular cardiomyocyte preparations. HL-1 cells were plated on microelectrode arrays and their spontaneous activity and theta was determined from field potential recordings. In heterocellular cultures of MSCs and HL-1 cells the beating frequency was attenuated (t(0h): 2.26 +/- 0.18 Hz; t(4h): 1.98 +/- 0.26 Hz; P < 0.01) concomitant to the intercellular coupling between MSCs and cardiomyocytes. In HL-1 monolayers supplemented with MSC conditioned media (ConM) or tyrode (ConT) theta significantly increased in a time-dependent manner (ConT: t(0h): 2.4 cm/s +/- 0.2; t(4h): 3.1 +/- 0.4 cm/s), whereas the beating frequency remained constant. Connexin (Cx)43 mRNA and protein expression levels also increased after ConM or ConT treatment over the same time period. Enhanced low-density lipoprotein receptor-related protein 6 (LRP6) phosphorylation after ConT treatment implicates the Wnt signaling pathway. Suppression of Wnt secretion from MSCs (IWP-2; 5 mu mol/l) reduced the efficacy of ConT to induce phospho-LRP6 and to increase theta. Inhibition of beta-catenin (cardamonin; 10 mu mol/l) or GSK3-alpha/beta (LiCl; 5 mmol/l) also suppressed changes in theta, further supporting the hypothesis that MSC-mediated Cx43 upregulation occurs in part through secreted Wnt ligands and activation of the canonical Wnt signaling pathway.